It’s difficult to think of any service (online or offline) that doesn’t use user’s data for their benefit. There generally has to be an input, in order for there to be beneficial output i.e. to rent your flat, you have to provide your telephone number, bank account details etc. to a letting agent / your landlord.
Hopefully you trust your bank to be custodians of your data. If you don’t then you shouldn’t be banking with them either. You mentioned privacy in your earlier post but what we’re looking at here is an algorithm scanning your data & saying if: direct debit to British Gas then: send recommendation, just as your existing bank has a rule like if: balance less than £20 then: send text alert, that’s all.
I can’t see a reason why the fact that the output is adverts would be more concerning. If the issue is that you don’t want to receive adverts then that’s fine - you can opt out.
One of Monzo’s specific aims is to use user’s data for their benefit, for example using your location data (opt in) to figure out your journey history & request a refund from TFL if you forgot to tap out when you left a station & were charged the maximum fare as a result. They already do something similar with the ‘welcome to [country]’ notifications.
The output might be different (it’s not an advert) but the process is almost exactly the same. This sort of use of user’s data (which doesn’t expose the user in any way) is key in order to create ‘magical’ experiences that delight the user. If you’re concerned about this sort of thing then maybe Monzo’s not for you & you should use a traditional bank. But even they will catch up to this sort of thing eventually.
So when you suggest that this is an unacceptable use of customer’s data, I’m trying to understand which aspect you consider unacceptable? Could you please explain what potential outcome you’re anticipating & therefore worrying about?